1. Field of the Invention
The present invention generally relates to an electronically controlled pneumatic (ECP) end of train (EOT) pneumatic emulation system and, more particularly, to a pneumatic emulation system which allows full train speed operation of standalone ECP train units with non-ECP equipped locomotives.
2. Background Description
Air brakes are the most commonly used brakes for freight trains. These brakes use changes compressed air pressure to control the operation of the brakes at each car along the train. A “brake pipe” connects all of the cars in the train and the locomotives, with the locomotives supplying the pressurized air to the brake pipe. The brake pipe may extend upwards of one mile or longer and provide the necessary air pressure to the brakes of each car of the train for braking operations.
In the most typical brake application systems, the brake control is actuated from a “driver's brake valve”. The driver's brake valve allows air to be fed into the brake pipe or released from the brake pipe during the braking operations. A distributor or “triple valve” located on each car also monitors the pressure in the brake pipe such that when brake pipe pressure falls below a certain level, the distributor allows air from an auxiliary reservoir to pass to the brake cylinders in order to activate the brakes of each train car. However, when the brake pipe pressure rises above a certain level, the distributor releases the air from the brake cylinders and recharges the auxiliary reservoir for the next braking application.
As is known to one skilled in the art, such long brake pipe lengths pose serious obstacles that must be overcome, such as, for example, controlling the air pressure along the entire length of the brake pipe in order to ensure adequate braking of the freight train. In order to address this problem, end-of-train (EOT) units were developed to monitor the air pressure within the brake pipe at the last car of the freight train. These EOT units are coupled to the locomotive via a radio link or other communication link so that the EOT unit can monitor brake pipe pressure and communicate such information to the engineer in the locomotive. Another problem of conventional brake systems using pneumatic control system is slow propagation rates of the compressed air along the brake pipe which reduces the braking efficiency of the train as well as the inability for graduated release. To address this problem, EOT units were modified to provide two-way communication between the locomotive and the EOT unit. The EOT unit was provided with a valve that could be actuated by command from the locomotive so as to vent the brake pipe to atmosphere in emergency braking situations, reducing by half the propagation rate of the emergency brake operation.
In order to solve the problem of slow propagation rates for service brake operation as well as generally improving the responsiveness of the braking application, Electronically Controlled Pneumatic (ECP) systems are implemented for use with the braking application system. ECP systems employ electrically controlled valves at each car in the train. Service (and emergency) brake operation is initiated and controlled by an electrical signal, which is typically propagated along a trainline that extends the entire length of the train, although a wireless link can also be used.
Currently, ECP system implementation has begun as overlay systems, but there is a desire to move to “all electric” service operations. This is primarily driven by the extra costs associated with the need to support both pneumatic and ECP brake application systems on each train car of the train consist. At the present time there are two alternative approaches for providing all electric ECP operation:                Standalone ECP; and        Emulation Capability ECP.        
The lowest cost implementation in ECP systems is the “standalone” system, which does not include the extra two valves needed for providing pneumatics emulation capability (quick service and quick release). At the present time, the standalone system is desirable for captive fleets, where a relatively small number of locomotives can be equipped for ECP operation. However, implementation of ECP systems on major Class 1 railroads is more challenging due to the difficulty in dedicating locomotives for ECP operation prior to equipping the entire fleet.
The ECP system may be retrofitted to trains (including the locomotive and EOT unit) while using conventional air brake pipes, and may operate individual valves in order to control the brakes of each train car of the train consist. This retrofitting may include providing a control system hardwired to each of the trains via a cable extending the length of the train as well as a communication link and control system housed in the locomotive. In operation, the ECP control unit codes and sends signals to all of the cars in the train in order to control the braking operations. Once the individual cars receive the signals, the compressed air from the reservoirs is released in order to activate the brake cylinder until a desired cylinder pressure is achieved in each of the individual cars. Microprocessors on each of the cars continuously monitor brake cylinder pressure against leakage and maintain the desired pressure. Thus, since there are no flow controls and the like, a theoretically instantaneous reaction from all cars in the train is possible, thereby making ECP controlled brakes very responsive (i.e., a change in air pressure of the brake pipe does not have to propagate from the beginning of the train to the end of the train).
A drawback to ECP systems is the cost of implementing the equipment for an entire fleet such as, for example, retrofitting the locomotive with control units and transceivers and each car with sensors, control valves and the like. Moreover, the standalone ECP systems, without emulation capability, still need to have a level of “limp home” capability to accommodate cases where the only available locomotives are not ECP equipped, or there is an in-route failure of the ECP head-end-unit (HEU) hardware. Unfortunately, without having quick service and release capabilities, the ability to emulate pneumatic brake operation is quite limited, and would result in severe speed restrictions probably in the area of 20 mph. This would not be acceptable for planned operation with non-ECP equipped locomotives for any significant distances.